In regard to the shape (carcass line) of a carcass ply in a tire axial direction cross section, structures combining plural carcass lines having different radii of curvature have been disclosed (see patent documents 1 and 2). Further, a technology that improves fatigue resistance with respect to compression input by optimizing the twist structure of steel cords used in carcass plies has also been disclosed (see patent document 3).    Patent Document 1: JP-A No. 6-156011    Patent Document 2: JP-A No. 8-142602    Patent Document 3: JP-A No. 11-11107